PURPOSE: To ensure the accurate division of voltage even to a faint signal, by applying the difference between an output signal supplied from the 1st attenuator and the output signal of a circuit to the 2nd attenuator.

CONSTITUTION: If the DC component is larger enough than the AC component of an input signal, an output signal has only the DC component for a low-pass filter 1. The input/output characteristics of a variable attenuator 2 show the function characteristics having a control signal (x) as a parameter. The difference of DC component between the output signal of the attenuator 2 and the signal given from an output terminal is detected and amplified at an error amplifier 3. This difference can be set at 0 if the amplification factor of the amplifier 3 is sufficiently large. In other words, the characteristics of a variable attenuator 4 which is controlled by the output signal of the amplifier 3 can be set identical with the function characteristics of the function characteristics of the attenuator 2. The characteristics of the attenuator 2 is obtained digitally by a microcomputer which generates the function characteristics to the parameter.